Central pumping and energy recovery in a reverse osmosis system

ABSTRACT

A reverse osmosis system includes a plurality of feed pumps each having a feed pump input and a feed pump output, an input manifold in fluid communication with the feed pump inputs and a membrane feed manifold in fluid communication with the feed pump output. The system also includes a plurality of membrane chambers each in fluid communication with the membrane feed manifold and generating a permeate output and a brine output, each brine output in fluid communication with a brine manifold. The system further includes a plurality of booster devices each having a turbine portion with a turbine input in fluid communication with the brine manifold and a pump portion having a booster device pump input and a booster device pump output, each booster device pump output in fluid communication with the membrane feed manifold. The system includes a pump input manifold in fluid communication with the booster device pump input. The system also includes a medium pressure pump in fluid communication with the input manifold and the pump input manifold.

RELATED APPLICATION

This application is a non-provisional application of provisionalapplication 60/901,204, filed Feb. 13, 2007, the disclosure of which isincorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates generally to reverse osmosis systems,and, more specifically, to a multi-stage reverse osmosis system having acentralized pumping source.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Reverse osmosis systems are used to provide fresh water from brackish orsea water. A membrane is used that restricts the flow of dissolvedsolids therethrough.

Referring now to FIG. 1, a reverse osmosis system 10 is illustratedhaving a membrane array 12 that generates a permeate stream 14 and abrine stream 16 from a feed stream 18. The feed stream 18 typicallyincludes brackish or sea water. A feed pump 20 coupled to a motor 22pressurizes the feed stream 18 to the required pressure flow whichenters the membrane array 12.

The permeate stream 14 is purified fluid flow at a low pressure. Thebrine stream 16 is a higher pressure stream that contains dissolvedmaterials blocked by the membrane. The pressure of the brine stream 16is only slightly lower than the feed stream 18. The membrane array 12requires an exact flow rate for optimal operation. A brine throttlevalve 24 may be used to regulate the flow through the membrane array 12.Changes take place due to water temperature, salinity, as well asmembrane characteristics, such as fowling. The membrane array 12 mayalso be operated at off-design conditions on an emergency basis. Thefeed pumping system is required to meet variable flow and pressurerequirements.

In general, a higher feed pressure increases permeate production and,conversely, a reduced feed pressure reduces permeate production. Themembrane array 12 is required to maintain a specific recovery which isthe ratio of the permeate flow to feed flow. The feed flow or brine flowlikewise requires regulation.

A pretreatment system 21 may also be provided to pretreat the fluid intothe membrane array 12. The pretreatment system 21 may be used to removesolid materials such as sand, grit and suspended materials. Each of theembodiments below including those in the disclosure may include apretreatment system 21.

Referring now to FIG. 2, a system similar to that in FIG. 1 isillustrated with the addition of a feed throttle valve 30. Medium andlarge reverse osmosis plants typically include centrifugal-type pumps20. The pumps have a relatively low cost and good efficiency, but theymay generate a fixed pressure differential at a given flow rate andspeed of rotation. To change the pressure/flow characteristic, the rateof pump rotation must be changed. One way prior systems were designedwas to size the feed pump 20 to generate the highest possible membranepressure and then use the throttle valve 30 to reduce the excesspressure to meet the membrane pressure requirement. Such a system has alow capital cost advantage but sacrifices energy efficiency since thefeed pump generates more pressure and uses more power than is requiredfor a typical operation.

Referring now to FIG. 3, another system for solving the pressure/flowcharacteristics is to add a variable frequency drive 36 to operate themotor 12 which, in turn, controls the operation of the feed pump 20.Thus, the feed pump 20 is operated at variable speed to match themembrane pressure requirement. The variable frequency drives 36 areexpensive with large capacities and consume about three percent of thepower that would otherwise have gone to the pump motor.

Referring now to FIG. 4, a system similar to that illustrated in FIG. 1is illustrated using the same reference numerals. In this embodiment, ahydraulic pressure booster 40 having a pump portion 42 and a turbineportion 44 is used to recover energy from the brine stream 16. The pumpportion 42 and the turbine portion 44 are coupled together with a commonshaft 46. High pressure from the brine stream passes through the turbineportion 44 which causes the shaft 46 to rotate and drive the pumpportion 42. The pump portion 42 raises the feed pressure in the feedstream 18. This increases the energy efficiency of the system. Thebooster 40 generates a portion of the feed pressure requirement for themembrane array 12 and, thus, the feed pump 20 and motor 22 may bereduced in size since a reduced amount of pressure is required by them.

Referring now to FIG. 5, a basic low-cost scheme for a large reverseosmosis plant 50 is illustrated using reference numerals similar tothose of FIG. 1. In this embodiment, three reverse osmosis stages havingthree membranes 12 a, 12 b, and 12 c are used together with threethrottle valves 30 a, 30 b, and 30 c. Three brine throttle valves 24 a,24 b, and 24 c are coupled to the brine output 16 a, 16 b, and 16 c. Thefeed stream 18 is coupled to a feed manifold 52 which, in turn, iscoupled to each of the feed throttle valves 30 a-30 c. Each throttlevalve is used to provide feed fluid to each of the respective membrane12 a-12 c. The brine stream 16 a-16 c passes through the brine throttlevalves 24 a-24 c and into a brine manifold 54. The permeate streams arecoupled to a permeate manifold 56.

In a large reverse osmosis plant 50, the objective is to use a feed pumpwith the largest available capacity to achieve the highest possibleefficiency at the lowest capital cost per unit of capacity. The optimalcapacity of a membrane array 12 is usually smaller than the pumps.Therefore, a single-feed pump 20 may be used to multiple supply membranearrays 12. Such a configuration is called centralized feed pumping.Because each of the membranes has a variable pressure requirement,individual control using the throttle valves 30 a-30 c and 24 a-24 c maybe used. However, using throttle valves wastes energy. Also, theindividual membranes themselves may have their own pressure requirementsdue to the following level of the membranes which may vary over themembrane array.

Referring now to FIG. 6, a similar configuration to that of FIG. 5 isillustrated with the addition of a variable frequency drive used todrive the motor 22 and thus the pump 20. The variable frequency drive 60is used to develop enough pressure at the pump 20 to satisfy thepressure requirements of the membrane arrays with the highest pressurerequirement. The centralized pumping is partially offset by thedifficulty of customizing the fixed discharge pressure of the feed pumpto the variable pressure requirements of the multiple membrane arrays.Both of the configurations in FIGS. 5 and 6 require individualthrottling and, thus, the energy efficiency is limited.

Referring now to FIG. 7, an embodiment similar to that illustrated inFIG. 4 may include an auxiliary brine nozzle 70 that is controlled by abrine valve 72. Normal operating conditions of a reverse osmosis planmay require making variations in the brine flow and pressure to keep themembrane array operating at optimal conditions. The brine valve 72allows the brine flow to be increased to allow additional high pressurebrine to pass into the turbine portion 44. If less brine flow isrequired, the auxiliary brine valve 72 may be closed. The auxiliarybrine valve 72 may be manually closed or closed by a valve actuator.

Referring now to FIG. 8A, another prior art embodiment is illustratedthat includes a feed manifold 80 that receives low pressure feed fluid.The feed fluid may be provided from a pretreatment system 21 asillustrated in FIG. 1. In this embodiment, a plurality of feed pumps 20is illustrated. The components set forth may be provided in severalredundant systems. The components may be referred to without theiralphabetical designations. In particular, three pumps 20 a-20 c withcorresponding motors 22 a-22 c are provided. The pumps 20 provide fluidat a high pressure to a high-pressure feed manifold 82. For servicingpurposes, the pumps 20 a-20 c may be isolated and taken off line throughthe use of isolation valves 84 and 86. The isolation valve 84 may bepositioned between the low pressure feed manifold 80 and the pump 20.The isolation valve 86 may be positioned between the pump and the highpressure manifold 82.

The pumps 20, the motors 22, and the isolation valves 84 and 86 may bereferred to as the high pressure pump portion 90.

An isolation valve 92 may be positioned between the high pressuremanifold 82 and the membrane 12. Each of the membrane arrays 12 a-12 hmay include a corresponding input isolation valve 92 a-h. A permeateisolation valve 94 may be positioned at the permeate outlet of themembrane array 12. A throttle valve 93 may also be disposed at eachmembrane downstream of isolation valve 92 to permit regulation ofpressure for each membrane array 12. The throttle valves are labeled 93a-93 h. An isolation valve 96 may be located at the high pressure brineoutput of the membrane array 12. Each of the respective membrane arraysmay include a permeate isolation valve 94 and a brine isolation valve96. The membrane arrays 12 and the isolation valves 92-96 may bereferred to as the membrane array section 100 of the system.

The permeate outputs of the membranes 12 may all be in fluidcommunication with a low pressure permeate manifold 102 through thevalves 94. The high pressure brine output of the membranes 12 may be influid communication with a high pressure brine manifold 104.

A plurality of flow work exchangers (FWE) 110 may be in fluidcommunication with the high pressure brine manifold 104. The flow workexchanger 110 will be further described below in FIG. 8B.

One output of the flow work exchanger 110 provides a lowered pressurefrom the brine output to a drain 112.

The flow work exchanger 110 also has an input in fluid communicationwith the low pressure feed manifold 80. Each fluid work exchanger 110pressurizes the fluid received from the feed manifold 80 and provides ahigher pressure to the high pressure feed manifold 82. The flow workexchanger 110 thus draws feed fluid from the low pressure feed manifold80 and increases the pressure therein which is discharged into thehigher pressure feed manifold 82. Thus, the combination of the output ofthe pump portion 90 and the output of the energy recovery portion 120combine to provide the feed flow for the membrane portion 100.

The flow work exchanger 110 thus has two fluid input and two fluidoutputs. The fluid input to the flow work exchanger 110 from the brinemanifold 104 may include an isolation valve 122. The fluid input to theflow work exchanger 110 from the low pressure feed manifold 80 mayinclude an isolation valve 124. The brine output of the flow workexchanger 110 may include an isolation valve 126. The high pressureoutput of the flow work exchanger 110 may include an isolation valve128.

The isolation valves 122, 124, 126 and 128 allow the flow work exchanger110 to be removed from service without interrupting the operation of thesystem. In the configuration of FIG. 8, the flow work exchanger 110 canonly deliver a feed flow rate that is about equal to the brine flowrate. There is no possibility to increase or decrease the feed flowrelative to the brine flow.

Referring now to FIG. 8B, the flow work exchanger 110 is illustrated infurther detail. The flow work exchanger 110 may include electricalcontrol equipment 130, booster pumps 133 and other equipment 137, 138.The other equipment may include pistons, valves and pressure vessels.The various components within the flow work exchanger 110 may beconnected in various ways depending on the type of components used.

Improving the efficiency of reverse osmosis systems to reduce energyconsumption is a desirable goal.

SUMMARY

The present disclosure provides a reverse osmosis system that is costeffective to control variability in the system in a convenient andefficient manner.

In one aspect of the disclosure, a reverse osmosis system includes aplurality of feed pumps each having a feed pump input and a feed pumpoutput, an input manifold in fluid communication with the feed pumpinputs and a membrane feed manifold in fluid communication with the feedpump output. The system also includes a plurality of membrane chamberseach in fluid communication with the membrane feed manifold andgenerating a permeate output and a brine output, each brine output influid communication with a brine manifold. The system further includes aplurality of booster devices each having a turbine portion with aturbine input in fluid communication with the brine manifold and a pumpportion having a booster device pump input and a booster device pumpoutput. Each booster device pump output is in fluid communication withthe membrane feed manifold. The system includes a pump input manifold influid communication with the booster device pump input. The system alsoincludes a medium pressure pump in fluid communication with the inputmanifold and the pump input manifold.

In another aspect of the disclosure, a reverse osmosis system includes aplurality of feed pumps each having a feed pump input and a feed pumpoutput and an input manifold in fluid communication with the feed pumpinputs. The input manifold has a first pressure therein. The system alsohas a membrane feed manifold in fluid communication with the feed pumpoutput. The membrane feed manifold has a second pressure greater thanthe first pressure. The system also has a plurality of membrane chamberseach in fluid communication with the membrane feed manifold andgenerates a permeate output and a brine output. Each brine output influid communication with a brine manifold. A plurality of boosterdevices each has a turbine portion with a turbine input in fluidcommunication with the brine manifold and a pump portion having abooster device pump input and a booster device pump output. Each boosterdevice pump output is in fluid communication with the membrane feedmanifold. The system also includes a pump input manifold in fluidcommunication with the booster device pump input. The system alsoincludes a medium pressure pump in fluid communication with the inputmanifold and the pump input manifold. The medium pressure pump generatesa third pressure in the pump input manifold greater than the firstpressure but less than the second pressure.

In a further aspect of the disclosure, a method of operating a reverseosmosis system with a membrane chamber in communication with a membranefeed manifold and generating a permeate output and a brine output influid communication with a brine manifold, and booster devices eachhaving a turbine portion in fluid communication with the brine manifoldand a pump portion in fluid communication with a pump input manifoldincludes pumping feed fluid having a first pressure in an input manifoldto a second pressure greater than the first pressure into the membranefeed manifold, pumping feed fluid having the first pressure in the inputmanifold to a third pressure greater than the first pressure but lessthan the second pressure into a pump input manifold, communicating feedfluid at the third pressure to the pump portions of each booster device,increasing the second pressure in the membrane feed manifold using thepump portions of each booster device in response to a brine pressure ina brine manifold.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic view of a prior reverse osmosis system.

FIG. 2 is a schematic view of an alternate prior art reverse osmosissystem.

FIG. 3 is a schematic view of another prior art of a reverse osmosissystem.

FIG. 4 is another schematic view of a prior art configuration of areverse osmosis system.

FIG. 5 is another schematic view of a prior art configuration of areverse osmosis system.

FIG. 6 is another schematic view of a prior art configuration of areverse osmosis system.

FIG. 7 is a schematic view of a hydraulic pressure booster according tothe prior art.

FIG. 8A is a schematic view of a multistage membrane reverse osmosissystem according to the prior art.

FIG. 8B is a detailed diagrammatic view of the flow work exchanger ofFIG. 8A according to the prior art.

FIG. 9 is a schematic view of a reverse osmosis system according to thepresent disclosure.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses. Forpurposes of clarity, the same reference numbers will be used in thedrawings to identify similar elements. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A or Bor C), using a non-exclusive logical or. It should be understood thatsteps within a method may be executed in different order withoutaltering the principles of the present disclosure.

Referring now to FIG. 9, an embodiment similar to FIG. 8 with variouscomponents is illustrated. The same reference numerals are used for thesame components. In this embodiment, isolation valves 92, 94 and 96 andthrottle valves 93 may be associated with the membrane arrays 12 andisolation valves 84 and 86 may be associated with the pumps 20 in asimilar manner to that described above. The plurality of feed pumps 20and the membrane arrays 12 may also be configured the same as in FIG. 8.

In this embodiment, a medium pressure pump 200 driven by a motor 202,which in turn may be driven by a variable speed drive 204, is disposedwithin the low pressure feed manifold 80. A pump input manifold 222 mayhave an increased pressure from the low pressure feed manifold 80. Inaddition to or alternatively from the variable speed drive 204, athrottle valve 220 may be provided to regulate the pressure within theinput manifold. The medium pressure pump 200 may ultimately be used tochange the pressure at the feed manifold 82.

A booster device 212 used for energy recovery may be used instead of theFWE of FIG. 8A. Two booster devices are illustrated. Each booster device212 may include a pump portion 210 and a turbine portion 214. The pumpportion 210 may be in fluid communication with the pump 200 through thepump input manifold. The pump input manifold 222 has feed fluid therein.The turbine portion 214 has an input in fluid communication with thebrine manifold 104 and a low pressure output in communication with thedrain 112. The turbine portion 214 and pump portion may be coupledtogether with a common shaft 215 (or other coupling mechanism) so energyin the high pressure brine stream is captured to drive the pump portion210.

The brine manifold 104 may be in fluid communication with an auxiliarybrine manifold 230. The auxiliary brine manifold 230 and the brinemanifold 104 may have a brine control valve 232 therebetween. Thepressure in the auxiliary brine manifold 230 may be controlled andregulated using the brine control valve 232. This may be done manuallyor by actuator. The auxiliary brine manifold 230 is in fluidcommunication with the turbine portions 214 through an auxiliary nozzleor port 234. An isolation valve 236A may be used to regulate the flowand isolate or turn off the input to the auxiliary port 234A.

In operation, the medium pressure pump 200 pressurizes the feed from thelow pressure manifold 80 to an intermediate value higher than the feedinput manifold pressure 80. The intermediate value may be approximatelyor less than 25 percent of the membrane pressure. The medium pressurefeed fluid is provided to the energy recovery portion 120. Morespecifically, the feed fluid is provided to the feed pump 210 throughthe pump input manifold 222. The pump portion 210 increases thepressure. The turbine portion 214 of the booster device 212 recovers theenergy from the high pressure brine manifold 104 and increases thepressure of the feed fluid. Energy from the brine manifold 104 isconverted to drive the pump portion 210. The pressure of the output ofthe pump portion 210 may increase and allow variance to the pressure inthe membrane manifold 82. Changing the pressure in the manifold 82 maybe done by controlling the VFD 204 in communication with the motor 202and pump 200.

The auxiliary brine manifold 230 may be used to provide uniform pressureto each auxiliary nozzle 234 of booster devices 212. Each booster device212 may operate at the same brine flow and pressure and thus share inthe hydraulic load. One adjustment of the brine control valve 232 allowsthe brine flow to each booster device to be adjusted. This eliminatesindividual valve actuators and control valves which reduces the overallcost of the system. The isolation valves 122, 124, 126, 128 and 236allow the removal of a booster device without interruption to thesystem. It should be noted that the maximum flow through the auxiliarybrine manifold 230 may be less than a predetermined amount of the flowin the brine manifold 104 such as 15%.

The booster device 212 may be driven to provide a variable speed flowrate. However, the amount of pressure boost generated by the feed pumpportion 210 may likewise vary. A high feed flow decreases the pressureboost and likewise a low feed flow allows a higher pressure boost.Therefore, the feed flow through the pump portion can be controlled byregulating the pressure of the input manifold 222 after the pump 200.Thus, the control of the feed flow may be independent of the brine flow.The feed flow through the pump portion 210 may be varied over a range ofabout 25 percent through adjustment of pressure at the pump 200.

Another way in which to control the system is to use a brine flow meter250 on the low pressure brine manifold 252 leading to drain 112. Theflow meter generates a brine flow signal to a valve actuator on valve232 to regulate brine flow. A permeate flow meter 256 on the lowpressure permeate manifold 102 generates a permeate flow signal to VFD204 to regulate permeate production. In this way, only two flow metersare used to regulate the permeate production and brine flow because thefeed flow equals the brine flow plus the permeate flow. Whether thesystem just has one train or twenty trains, the control scheme is thesame. Also, if a membrane array or a feed pump is taken out of service,the resulting changes in brine and permeate flows generate a response toincrease speed of medium pressure pump 200 and/or open control valve 232to restore permeate and brine flows to the design values without anyintervention required by the operating staff.

Those skilled in the art can now appreciate from the foregoingdescription that the broad teachings of the disclosure can beimplemented in a variety of forms. Therefore, while this disclosureincludes particular examples, the true scope of the disclosure shouldnot be so limited since other modifications will become apparent to theskilled practitioner upon a study of the drawings, the specification andthe following claims.

What is claimed is:
 1. A reverse osmosis system comprising: a pluralityof feed pumps each having a feed pump input and a feed pump output; aninput manifold in fluid communication with the feed pump inputs, saidinput manifold having a first pressure; a membrane feed manifold influid communication with the feed pump output, said membrane feedmanifold having a second pressure greater than the first pressure; aplurality of membrane chambers, each in fluid communication with themembrane feed manifold and generating a permeate output and a brineoutput, each brine output in fluid communication with a brine manifold;a plurality of booster devices, each having a turbine portion having aturbine input in fluid communication with the brine manifold and a pumpportion having a booster device pump input and a booster device pumpoutput, each booster device pump output in fluid communication with themembrane feed manifold; a pump input manifold in fluid communicationwith the booster device pump input; a permeate manifold in fluidcommunication with each permeate output of the plurality of membranechambers; a permeate flow meter generating a permeate flow signal; and amedium pressure pump coupled to a motor and variable speed drive, saidmedium pressure pump communicating fluid from the input manifold to thepump input manifold, said variable speed drive controlling the mediumpressure pump to generate a variable third pressure in the pump inputmanifold greater than the first pressure and less than the secondpressure based on the permeate flow signal.
 2. A reverse osmosis systemas recited in claim 1 further comprising an auxiliary brine manifold influid communication with the brine manifold, each turbine portioncomprising an auxiliary input nozzle in fluid communication with theauxiliary brine manifold through a brine control valve.
 3. A reverseosmosis system as recited in claim 2 wherein the medium pressure pump isdisposed between the pump input manifold and the input manifold.
 4. Areverse osmosis system as recited in claim 1 further comprising anauxiliary brine manifold in fluid communication with the brine manifold,each turbine portion comprising an auxiliary input nozzle in fluidcommunication with the auxiliary brine manifold.
 5. A reverse osmosissystem as recited in claim 4 wherein said brine manifold has a firstflow rate and the auxiliary brine manifold has a second flow rate up toabout 15 percent of the first flow rate.
 6. A reverse osmosis system asrecited in claim 1 further comprising a motor coupled to the mediumpressure pump.
 7. A reverse osmosis system as recited in claim 6 furthercomprising a variable speed drive controlling the motor to generate thevariable third pressure.
 8. A reverse osmosis system as recited in claim1 further comprising an auxiliary brine manifold in fluid communicationwith the brine manifold, each turbine portion comprising an auxiliaryinput nozzle in fluid communication with the auxiliary brine manifoldthrough a brine control valve, said reverse osmosis system furthercomprising a low pressure brine manifold in fluid communication with aturbine portion output of each of the plurality of booster devices and alow pressure brine flow meter generating a brine flow signal, the brinecontrol valve controlled in response to the brine flow signal.
 9. Areverse osmosis system as recited in claim 1 wherein the third pressureis about 25 percent of the second pressure.
 10. A reverse osmosis systemas recited in claim 1 wherein the third pressure is less than 25 percentof the second pressure.
 11. A reverse osmosis system as recited in claim1 wherein a feed flow through the membrane feed manifold is controlledindependently of a brine flow in the brine manifold.
 12. A reverseosmosis system comprising: a plurality of feed pumps each having a feedpump input and a feed pump output; an input manifold having a firstpressure in fluid communication with the feed pump inputs; a membranefeed manifold having a second pressure in fluid communication with thefeed pump output; a plurality of membrane chambers, each in fluidcommunication with the membrane feed manifold and generating a permeateoutput and a brine output, each brine output in fluid communication witha brine manifold; a plurality of booster devices, each having a turbineportion having a turbine input in fluid communication with the brinemanifold and a pump portion having a booster device pump input and abooster device pump output, each booster device pump output in fluidcommunication with the membrane feed manifold; a pump input manifold influid communication with the booster device pump input; a permeatemanifold in fluid communication with each permeate output of theplurality of membrane chambers; a permeate flow meter generating apermeate flow signal; and a medium pressure pump coupled to a motor andvariable speed drive, said medium pressure pump communicating fluid fromthe input manifold to the pump input manifold, said variable speed drivecontrolling the medium pressure pump to generate a variable thirdpressure in the pump input manifold greater than the first pressure andless than the second pressure based on the permeate flow signal.
 13. Areverse osmosis system as recited in claim 12 further comprising anauxiliary brine manifold in fluid communication with the brine manifold,each turbine portion comprising an auxiliary input port in fluidcommunication with the auxiliary brine manifold.
 14. A reverse osmosissystem as recited in claim 12 further comprising an auxiliary brinemanifold in fluid communication with the brine manifold, each turbineportion comprising an auxiliary input port in fluid communication withthe auxiliary brine manifold through a brine control valve.
 15. Areverse osmosis system as recited in claim 14 further comprising a lowpressure brine manifold in fluid communication with a turbine portionoutput of each of the plurality of booster devices and a low pressurebrine flow meter generating a brine flow signal controlling the brinecontrol valve.